The present invention relates generally to a magnetic tape cassette, especially adapted to recording and reproducing pulse code modulated (PCM) signals. More specifically, the invention relates to a magnetic tape cassette provided with a tape protective closure covering a front opening through which a magnetic tape is extracted and accessed, and a locking mechanism for locking the closure open when the cassette is in use and locking it closed when not in use.
Recently, various recording and reproducing apparatus have been developed which convert analog signals, such as audio signals and the like into digital signals, e.g. PCM signals, which are then recorded on and reproduced from magnetic tape serving as a recording medium. Some of these apparatus employ rotary heads so as to achieve a relatively high recording density. Recording and reproducing apparatus specifically designed to record and reproduce PCM signals and employing a rotary head will be referred to as "PCM recorder" throughout the disclosure. A PCM recorder, at first, pulls a loop of a magnetic tape out through a front opening of the cassette and winds the tape around a rotary drum accommodating the rotary head and then the recording and reproducing is performed. In such digital recording and reproducing systems, oily deposits, such as fingerprints or the like, and/or dust adhering to the tape surface may cause dropout of reproduced signals.
Various approaches have been tried to protect the magnetic recording medium. For example, a closure lid may be used to retractably cover the front end opening of the cassette, through which the tape is extracted for access by a rotary head. This closure lid is held closed while the tape is not in use and is moved to an open position when the cassette is inserted into the PCM recorder. In this earlier approach, a drawback may be encountered when the closure lid is unintentionarily or accidentally opened, exposing the tape to oily fingerprints, dust and so forth while it is not in use. A locking mechanism which can conveniently lock the closure lid in its open and closed positions, could resolve this problem.